This study of aminocyclitol antibiotics is restricted by their clinical toxicity. This study is directed towards the understanding of the mechanism of interaction of these antibiotics with membranes, as well as the nature of aminocyclitol toxicity. Binding of the antibiotics to isolated membrane vesicles in the kidney and the intestine is being studied. The uptake of these radioactively labeled antibiotics into vesicles prepared from kidneys, intestine and bacteria are compared. Preliminary evidence shows that the antibiotic is both bound to vesicle preparations and assimilated by them. The antibiotic also penetrates into the intestinal cell but is modified there to a biologically inactive form.